1. Field of the Invention
The present invention refers to a system for determining offsets (bias) of measuring instruments (included electronic adaptation and interface), in particular measures with null or constant mean value. The present invention is applicable to all sensors, complete of electronic interfacing, used to measure variations of one physical phenomenon: there is a steady state condition and a variation respect to this condition. When the interest is the real value of physical phenomena it is necessary to use a sensor with adequate absolute precision; it isn't possible to subtract bias (offsets). If the interest is the variation respect to the steady state value, it is possible to estimate offsets and to applier the present invention. The known that the physical phenomena moves respect a constant mean value allows the estimation of offsets (bias) and the measure, with the presented method, of physical phenomena with very high precision (higher the sensors used). The present invention further refers to a process for determining offsets of measuring instruments through a system according to the present invention. It is applicable to all type of sensors: linear or angular position, speed and acceleration sensors, pressure, temperature, rate of flow, heading, etc. to measure the variation with very high resolution or with a precision better than the original physical sensor. The method allows estimating total bias (due to sensor, its physical arrangement and its conditioning and adapting electronic circuits)
2. Background Information
As known, any measuring instrument or sensor is substantially affected by an offset composed of two types of errors:                systematic measuring errors, constant and dependent from the physical principle used and the sensibility of the instrument or sensor itself;        slowly-varying errors, dependent from environmental and use conditions in which the instrument or sensor has to operate, such as for example temperature, pressure, humidity, instrument and electronic ageing, height variation on sea level (for accelerometers measure), etc.        
When measures performed by the measuring instrument have a null or constant mean value, or point out the difference with respect to a fixed position, it is possible to determine the measuring error rather accurately, and thereby clean the measure itself from the global error, as sum of fixed and slowly-varying errors with respect to the dynamics of the system to which it is applied.
In particular, for example, it is also known in the art that angular speed sensors have a particularly important role in stabilisation systems for roll and pitch in boats and other different systems, since the rolling speed has a major weight on the efficiency of adjustments through fins. In order to be able to use sensors with acceptable costs, currently angular speed sensors are used with a ±50°/s full scale, while the working range for measures is on the maximum order of magnitude of 2 or 3°/s. Every sensor therefore has a systematic error and a slowly-varying error that depends on environmental temperature, ageing, and other above-mentioned conditions: this error is typically on the order of 1%. In this case the measuring error is of the same order of magnitude of the amount that has to be measured, and it would therefore be essential to clean the sensor from fixed and (slowly with respect to the phenomenon that has to be detected) varying errors automatically, and obtain a measure with a better accuracy than the one obtained by the pure sensor. However, without the estimation and subtraction of this error, it is not possible to use the sensor importantly and with relevant efficiency with respect to other measures and, consequently, the regulating systems, in which the sensor is used, cannot have relevant performances.
Similar example is the problem of estimation of the vertical movement of an object. To make a good estimation of vertical movement is necessary to extract'the bias of accelerometer measure; this is possible, with the present invention, with the estimation and subtraction of the bias. The offset of accelerometers changes with temperature, sensor ageing, height respect the sea level, etc. The present invention allows the correct calculation of bias and its subtraction.
Documents U.S. Pat. No. B1-6,498,409 and U.S.-A1-2010/164425 disclose systems according to the preamble of claim 1.